Braking apparatus

ABSTRACT

A braking system for a vehicle wheel which system comprises a reservoir, and a pump pumping liquid from the reservoir through a conduit and back to the reservoir in relation to the vehicle wheel speed. A progressively closable restriction is provided downstream of a connection to the brakes so liquid pressure upstream of the closable restriction may be increased to apply the brakes. A leakage conduit is provided to by-pass the closable restriction and the connection, and incorporates a variable restriction the opening of which increases with increased vehicle wheel speed. Means are provided to sense the rate of change of wheel rotational speed, and when the rate exceeds a predetermined value, a pressure reducing valve is operated to relieve pressure applied to the brakes.

United States Patent [1 1 Hodge et a1. July 3, 1973 41 BRAKING APPARATUS3,672,731 6/1972 Koivunen 303/21 F [75] Inventors: Peter Charles Hodge;George Frankl,

both f London, England Primary Lxaminer-M. Henson Wood, Jr. AssistantExaminer-John J. Love [731 Ass1gnee= Simms Group Research andAttorney-Watson, Cole, Grindle: & Watson Development Limited, London,England [57] ABSTRACT [22] F11ed: Jan. 18, 1972 A braking system for avehicle wheel which system 1 pp 218,752 comprises a reservoir, and apump pumping liquid from the reservoir through a conduit and back to thereser- [30] Foreign Application priority Data voir in relation to thevehicle wheel speed. A progres- Jan 21 1971 Great Britain 2 877, sivelyclosable restriction 18 provided downstream of a 'i connection to thebrakes so liquid pressure upstream of the closable restriction may beincreased to apply the CCll 303/21 brakes A leakage conduit is providedto m the 5 Fie'ld F 10 61 closable restriction and the connection, andincorpo- 2 g rates a variable restriction the opening of which increaseswith increased vehicle wheel speed. Means are [5 6] References Citedprovided to sense the rate of change of wheel rotational speed, and whenthe rate exceeds a predetermined UNITED STATES PATENTS value, a pressurereducing valve is operated to relieve 3,539,227 11/1970 Drutchas et a].303/10 X pressure applied to the brakes, 3,514,162 5/1970 Erlebach eta1. 303/21 F 3,661,427 5/1972 Hodge 303/21 F 8 Claims, 1 Drawing; Figureso 23 l B 4/ 2 B 2/ 45' (J R 29 v n 5 o o l 0 45 I 35 I 2 25 23 42 48 44l7 I8 36 i 1 BRAKING APPARATUS BACKGROUND OF THE INVENTION The inventionrelates to braking systems.

The invention is a modification of the invention described in U S Pat.application Ser. No. 16,286, now US. Pat. No. 3,661,427 dated May 9,1972 and commonly owned herewith in which there is described and claimeda braking system for a vehicle wheel comprising brake operating means, areservoir for liquids, a pump having a drive means which increases thepump throughput with increased wheel rotational speed, means to connectthe pump input with the reservoir, a conduit connecting the pump outputto the reservoir, a connection between the conduit and the brakeoperating means, brake applying means located downstream of theconnection and operable to add a restriction into the conduit so thatthe liquid pressure in the connection is increased, a leakage conduitarranged to t bypass the brake applying means, which leakage conduitincorporates a variable restriction to provide a variable restriction toliquid flow and a fixed restriction in series with the variablerestriction, and means to vary the variable restriction automaticallywith increased wheel rotational speed.

SUMMARY OF THE INVENTION With such a system, it is important that thebraking performance is constant over a wide wheel rotational speed bandand also serves to eliminate lock of the wheel over that band. It is anobject of the present invention to provide a system which operates overa wheel rotational speed band without loss of braking performance andprevents wheel-lock for all wheel rotationAl speeds in a band which iswider than that allowed by that system described in the aforementionedpatent. In accordance with this object, the invention provides a brakingsystem'for a vehicle wheel comprising;

a. brake operating means;

b. a reservoir for liquids;

c. a pump having drive means which increases the pump throughput withincreased wheel rotational speed;

d. means to connect the pump input with the reservoir;

e. a conduit connecting the pump output with the reservoir;

f. a connection between the conduit and the brake operating means;

g. brake applying means located downstream of the connection, andoperable to add a restruction into the conduit so that the liquidpressure in the connection is increased;

h. a leakage conduit arranged to bypass the brake applying means, Whichleakage conduit incorporates a variable restriction to provide avariable restriction to liquid flow; l v I i. means to vary the variablerestriction automatically with increased wheel rotational speed;

j. means to sense the rate of change of wheel rotational speed;

k. pressure reducing means operable by the means to sense the rate ofchange of wheel rotational speed when the rate of change exceeds apredetermined value, said pressure reducing means being operable toreduce the pressure applied to the brake applying means.

Said means to sense the rate of change of wheel rotational speed maycomprise means to produce a fluid pressure difference which is dependenton the rate of change of wheel rotational speed.

The pressure reducing means may comprise valve means connected inparallel with the liquid leakage path, the valve means being operable bysaid pressure difference.

In the last described arrangement, the valve means may comprise ahousing, and a shuttle slidable within said housing, the two sides ofthe shuttle being connected across the pressure difference such thatwhen the pressure difference exceeds a predetermined value, the valvemeans opens.

In the case in which the leakage conduit includes a variable restrictioncomprising a cylinder, a shuttle slidable within the cylinder andproviding in combination therewith the variable restriction, a furtherrestriction in the main delivery path from the pump to sense the outputprovided by the pump, the two sides of the shuttle being open to thepressures at the two sides of the further restriction respectively andin which a damping restriction is provided in the path between the highpressure side of the further restriction and shuttle, one

of the sides of the pressure reducing valve means may I be connected tothe high pressure side of the further restriction and the other of thesides of the pressure reducing valve means may-be connected to thevariable restriction shuttle side of the damping restriction.

In the last described arrangement spring means may be provided to biasthe shuttle of the variable restriction towards the end of its cylinderwhich is connected to the damping restriction.

The spring means may comprise a conical coil spring having apredetermined load/extension characteristic,

The pressure reducing valve means may have spring means to bias itsshuttle towards a position in which the valve is closed, the pressuredifference being applied to the pressure reducing valve means to openthe valve.

BRIEF DESCRIPTION OF THE DRAWINGS The following is a description of onepreferred embodiment of the invention, given by way of example,reference being made to the accompanying drawing which showsdiagrammatically a braking system for a vehicle.

DESCRIPTION OF PREFERRED EMBODIMENT The braking system shown in theaccompanying drawing is similar to that shown and described in theaforementioned patent, and parts common to both systems are given likereference numerals.

Referring to the drawing, the system comprises a brake pedal 1 connectedto a master cylinder (not shown) which, on depression of the pedal 1,pumps fluid through a line 2 to acylinder 4. The cylinder 4 has a valvemember 5 mounted for reciprocation therein and in fluid tightrelationship therewith, there being an axial conduit 6 in the valvemember 5 communicating with an annular groove 7 such that fluid pumpedby the master cylinder may pass through the conduit 6 and annular groove7 into a conduit 10 communicating with a side of the cylinder 4 when thevalve member is in the position shown. The conduit 10 communicates witha further conduit 11 and thereafter to the brake circuit of a wheel orwheels (not shown) of the vehicle. A spring 9 urges the valve member tothe position shown.

A pump 15, having a throughput substantially proportional to wheel speedand substantially independent of output pressureover the operation speedrange, such as transfer, piston or gear pump, is arranged to draw brakefluid from a tank 13 having a filter 14 mounted therein. The pump isdriven by a road wheel having a braking system connected to the conduit11. The pump 15 is arranged to pump brake fluid along a conduit 16,through a sensing restriction 17, into conduit 29 and then conduit 28via conduit 33, in which latter conduit is located a valve comprising aconical portion 8 of the valve member 5 and a co-operating portion ofthe cylinder 4. A pressure relief valve device of known design isindicated at 35 and connects conduit 29 to conduit 28. A cylinder 30having a plug 31 mounted therein and biased to one end of the cylinderby spring 32 is connected to the conduit 29 such that a rise in pressurein conduit 29 causes the plug 31 to move against the ac tion of thespring 32 and causes a substantially similar pressure rise of the fluidin conduit 11 to apply the brakes of the road wheel or wheels.

The sensing restriction 7 in conduit 16 results in a differential in thepressure, when the pump is pumping fluid along conduit 16, of fluid in aconduit 18 and a conduit 19 connecting into the conduit 16 and conduit29 each side respectively of the restriction 17, the conduits 18 and 19being connected to each end respectively of a control valve deviceindicated at 20. The conduit 18 is provided with a damping restriction36.

A shuttle 22 is housed within the bore of the control device 20 and hastapered flats 23 provided on its surface in a manner similar to thatdescribed in the aforementioned patent. The bore has an annular groove25 disposed part way between its ends, to which groove there isconnected a conduit 26 communicating with the conduit 28. The shuttle 22is provided with a bore 21 from its left hand end (in the drawing) whichcommunicates with the outer surface of the shuttle 22 adjacent thetapered flats 23, so that a restriction is provided to fluid passingfrom conduit 19 to conduit 26, the opening of the restriction beingdependent on the position of the shuttle 22 in the bore. The controldevice 20 differs from that described in the aforementioned patent inthat a conical coil spring 40 is provided to urge the shuttle 22 towardsthe right (in the drawing), the spring having a predeterminedload/deflection characteristic, which may be linear or non-linear.

A brake pressure reducer valve 41 is provided, which is arranged toprovide a path for fluid from conduit 29 into conduit 28 under certainconditions of operation as described below. The brake pressure reducervalve 41 comprises a shuttle 42 reciprocable within a housing the lefthand end (in the drawing) of the shuttle 42 being in communication withthe right hand side of the shuttle 22 by means of a conduit 43, and theright hand end of the shuttle 42 being in communication with the conduit16 by means of a-conduit 44. The shuttle 42 is urged towards the lefthand end of its housing by means of a helical coil spring 45.

The shuttle 42 of the brake pressure reducing valve 41 has an annulargroove 46 formed on its surface, there being a conduit 47 connected tothe conduit 20 and in communication with the space defined by the groove46. The bore of the housing in which the shuttle 42 is mounted isprovided with an outwardly extending annular groove 48, there being aconduit 49 connecting the conduit 28 to the annular groove 48. Theannular groove 48 is disposed in the cylinder adjacent the connection ofconduit 47 with the bore such that the groove 46 in the shuttle 42 mayplace the conduit 47 in communication with the conduit 49 when theshuttle 42 is moved to the right, to permit fluid to be pumped alongconduit 47 into conduit 49 and thence into conduit 28. I

The brake system operates generally in a similar manner to thatdescribed in the patent cited earlier herein in that, when the roadwheel rotates, fluid is pumped by pump 15 along conduit 16, throughorifice 17 into conduit 29, and is then returned into the reservoir 13through conduit 33 and conduit 28. in order to actuate the brakes, thepedal 1 is depressed which initially pumps brake fluid into the cylinder4 through conduit 6 into conduit 10 and conduit 1 l to actuate thebrakes. After this initial pumping of fluid, the valve member 5 is movedagainst the action of spring 9 so that conduit 10 is placed out ofcommunication with conduit 2 and so that the tapered portion 8 of thevalve member 5 co-operating with the cylinder 4 places a restriction inthe path of fluid pumped between conduicts 33 and 28 respectively. Thiscauses the pressure of fluid pumped along conduit 29 to rise, so thatthe plug 31 is moved against the action of the spring 32 to increase thepressure in conduit 1 1 thereby further applying the brakes to the roadwheel or wheels.

With high rotational wheel speeds, a relatively high differentialpressure is generated by pump 15 across restriction 17. This forces theshuttle 22 towards the lefthand side of its housing against the actionof spring 40 and the relatively large extent of the opening provided bythe flats 23 then in communication with annular groove 25 permits fluidto be pumped from conduit 29 through conduit 19 into conduit 26 and theninto conduit 28. At low rotational wheel speeds, the shuttle 22 is urgedby the spring 40 towards the right since only a low differentialpressure is generated across restriction 17. The load/deflectioncharacteristics of the conical coil spring 40 are arranged such that therate of movement of the shuttle 22 is in direct proportion to the rateof acceleration or deceleration of the wheel driving the pump 15. Duringdeceleration of the wheel driving the pump 15 and the consequentialmovement of the shuttle 22 to the right,the orifice 36 resists flow offluid from conduit 43 into conduit 16, and hence there is a pressurerise in conduit 43. When the pressure difference between that in conduit43 and that in conduit 44 (which is substantially the output pressure ofthe pump 15) rises above a predetermined value and is sufficient to movethe shuttle 42 to the right against the action of the spring 45, conduit47 is placed in communication with conduit 49 and the pressure inconduit 29 is relieved. This relieves the total pressure applied to theplug 31, and consequently the brakes on the road wheels are released toa certain extent. This permits the road wheel to start rotating at ahigher rate again, and the output of the pump 15 will rise once more sothat the pressure difference between conduits 43 and 44 will fall, thusclosing the brake pressure reducer valve.

It will be appreciated. that with the above described system, if theroad wheel driving the pump 15 is decelerated at a rate greater than apredetermined value (for example, if the wheel locks suddenly whilstbeing braked) the brake pressure reducing valve 41 will operate torelieve pressure in the conduit 29 so that the brakes are automaticallyreleased to a certain extent, whereafter the wheel may commence torotate again.

We claim:

1. A braking system for a vehicle wheel, comprising:

a. brake operating means;

b. a reservoir for liquids;

c. a pump having drive means which increases the pump throughput withincreased wheel rotational speed;

d. means to connect the pump input with the reservoir;

e. a conduit connecting the pump output with the reservoir;

f. a connection between the conduit and the brake operating means;

g. brake applying means located downstream of the connection, andoperable to add a restriction into the conduit so that the liquidpressure in the connection is increased;

h. a leakage conduit arranged to bypass the brake applying means, whichleakage conduit incorporates a variable restriction to provide avariable restriction to liquid flow;

i. means to vary the variable restriction automatically with increasedwheel rotational speed;

j. means to sense the rate of change of wheel rotational speed;

k. pressure reducing means operable by the means to sense the rate ofchange of wheel rotational speed, when the rate of change exceeds apredetermined value, said pressure reducing means being operable toreduce the pressure applied to the brake applying means.

2. A braking system as claimed in claim 1, in which said means to sensethe rate of change of wheel rotational speed comprises means to producea fluid pressure difference which is dependent on the rate of change ofwheel rotational speed 3. A braking system as claimed in claim 2 inwhich the pressure reducing means comprises valve means connected inparallel with the liquid leakage path, the valve means being operable bysaid pressure difference.

4. A braking system as claimed. in claim 3, in which the valve meanscomprises a housing, and a shuttle slidable within said housing, the twosides of the shuttle being connected across the pressure difference suchthat when the pressure difference exceeds a predetermined value, thevalve means opens.

5. A braking system as claimed in claim 4, and in which the leakageconduit includes a variable restriction comprising a cylinder, and ashuttle slidable within the cylinder and providing in combinationtherewith the variable restriction, a further restriction in the maindelivery path from the pump to sense the pump throughput, the two sidesof the shuttle being open to the pressures at the two sides of thefurther restriction respectively there being a damping restrictionprovided in the path between the high pressure side of the furtherrestriction and shuttle, wherein one of the two sides of the pressurereducing valve means is connected to the high pressure side of thefurther restriction and the other of the sides of the pressure reducingvalve means is connected to the variable restriction shuttle side of thedamping restriction.

6. A braking system as claimed in claim 5, in which spring means areprovided to bias the shuttle of the variable restriction towards the endof its cylinder which is connected to the damping restriction.

7. A braking system as claimed in claim 6, in which the spring meanscomprises a conical coil spring having a predetermined load/extensioncharacteristic.

8. A braking system as claimed in claim 4, in which the pressurereducing valve means has spring means to bias its shuttle towards aposition in which the valve is closed, the pressure difference beingapplied to the pressure reducing valve means to open the valve.

1. A braking system for a vehicle wheel, comprising: a. brake operatingmeans; b. a reservoir for liquids; c. a pump having drive means whichincreases the pump throughput with increased wheel rotational speed; d.means to connect the pump input with the reservoir; e. a conduitconnecting the pump output with the reservoir; f. a connection betweenthe conduit and the brake operating means; g. brake applying meanslocated downstream of the connection, and operable to add a restrictioninto the conduit so that the liquid pressure in the connection isincreased; h. a leakage conduit arranged to bypass the brake applyingmeans, which leakage conduit incorporates a variable restriction toprovide a variable restriction to liquid flow; i. means to vary thevariable restriction automatically with increased wheel rotationalspeed; j. means to sense the rate of change of wheel rotational speed;k. pressure reducing means operable by the means to sense the rate ofchange of wheel rotational speed, when the rate of change exceeds apredetermined value, said pressure reducing means bEing operable toreduce the pressure applied to the brake applying means.
 2. A brakingsystem as claimed in claim 1, in which said means to sense the rate ofchange of wheel rotational speed comprises means to produce a fluidpressure difference which is dependent on the rate of change of wheelrotational speed.
 3. A braking system as claimed in claim 2 in which thepressure reducing means comprises valve means connected in parallel withthe liquid leakage path, the valve means being operable by said pressuredifference.
 4. A braking system as claimed in claim 3, in which thevalve means comprises a housing, and a shuttle slidable within saidhousing, the two sides of the shuttle being connected across thepressure difference such that when the pressure difference exceeds apredetermined value, the valve means opens.
 5. A braking system asclaimed in claim 4, and in which the leakage conduit includes a variablerestriction comprising a cylinder, and a shuttle slidable within thecylinder and providing in combination therewith the variablerestriction, a further restriction in the main delivery path from thepump to sense the pump throughput, the two sides of the shuttle beingopen to the pressures at the two sides of the further restrictionrespectively there being a damping restriction provided in the pathbetween the high pressure side of the further restriction and shuttle,wherein one of the two sides of the pressure reducing valve means isconnected to the high pressure side of the further restriction and theother of the sides of the pressure reducing valve means is connected tothe variable restriction shuttle side of the damping restriction.
 6. Abraking system as claimed in claim 5, in which spring means are providedto bias the shuttle of the variable restriction towards the end of itscylinder which is connected to the damping restriction.
 7. A brakingsystem as claimed in claim 6, in which the spring means comprises aconical coil spring having a predetermined load/extensioncharacteristic.
 8. A braking system as claimed in claim 4, in which thepressure reducing valve means has spring means to bias its shuttletowards a position in which the valve is closed, the pressure differencebeing applied to the pressure reducing valve means to open the valve.